When grains are grown in the fields, the final quality is very dependent on the climate. If bad weather persists, and/or it is very windy so-called layers are produced, which often result in that the grains possess a high diastatic activity. High diastatic activity means that enzymes are produced/synthesised within the grains, which breaks down the starch during the use of the grain within the food industry or baking in households.
One way to screen the quality of the grains after harvest is to use the so-called Falling Number, which is a number obtained by a method which measures the diastatic activity. A high Falling-Number implies low diastatic activity and viceversa, which means that, grains obtaining a low Falling-Number has a high enzymatic activity and has been growing under bad conditions in the field. When high enzyme activity is prevalent, the microbial contamination level in the grains is most often high. Grains possessing high diastatic activity and a high microbial contamination level is not suitable for the production of flour to be used in food products, but is used instead for the production of animal feed, which reduces the economic value for the farmer.
Heat treatment of flour is one way to reduce enzymatic activity. However, high heat treatments result in colour changes and taste changes of the flour, as well as clumps of the flour. Furthermore, reduction of the microbial level is not satisfactory since the use of heat treatment has to be conducted in a sufficiently dry environment to avoid problems such as gelatinisation of starch within the flour. If this happens, the basic properties of the flour become altered. It is previously known that a reduction of microbes takes place more efficiently in the presence of water. To sterilise dry flour, using heat only, requires keeping the flour at about 180° C. for about 3 hours. This negatively affects the flavour, colour and the starch water absorbing capacity.
Another method to reduce the number of bacteria is to irradiate with gamma-rays. However, from the consumer's viewpoint, the technology is intuitively negative, which has resulted in negligible use of this method in industry, even though it is permitted within the EU and by the Swedish Food Agency to be used to reduce the bacterial number in spices. Products may also be sterilised by other known techniques like, fumigation using, for example, ethylene oxide, propylene oxide and sulphur dioxide. The first two mentioned gases lead to formation of toxic products, such as chlorohydrins, which is why the method using fumigation is forbidden in more and more countries all over the world. Sulphur dioxide is very toxic, and forms a hazard to the industrial staff, who have to perform the fumigation. A common example of the use of this method is the conservation of different fruitpulp masses. Sulphur dioxide is also regarded as an allergen, and has to be declared on the food label as such.
Surfaces have, since the beginning of the 1900's, been disinfected with ethanol (e.g. 70% volume/volume), both within healthcare and the food industry. Ethanol of 70% strength has proven to be effective towards vegetative bacteria, but insufficiently effective towards bacteria in the spore stages, which survive the treatment. Since these spores even survive the heat treatment to which the flour is exposed to during the baking process this method is far from satisfactory. At the same time, the use of ethanol does not contribute to a reduction of excessive enzymatic activity in the flour.
So far sterilising processes using ethanol have been focusing on batch sterilising systems which have the drawbacks that after each batch the complete system need to be cleaned and the process restarted. A huge draw back, which result in that it is not suitable to use in a commercial production plant. Further on, a number of techniques to minimize microorganisms in powders and flours are claimed to sterilize, even though the techniques do not actually sterilize, since these processes result in powder/flour that still contains spores etc. These techniques include known batch- and continuous production techniques and may sometimes involve ethanol.
In order to prepare a sterile liquid mixture with long shelf life the flour should be sterile before mixing with a sterile liquid. If spores remain in the flour, these spores can grow to bacteria after it has been mixed with the liquid resulting in a non-sterile liquid with reduced shelf life. The common UHT technique to sterilize liquids is not suitable for liquids containing flour since the starch will gelatinize resulting in a product without remaining baking properties.
The present invention provides a new process, which enables the possibility to sterilise flour in a closed system continuously. The method is also an effective method to sterilise the flour without severely changing the properties of the flour, such as the baking properties of the starch in the flour. The method further reduces the enzymatic activity within the flour and eliminates unfavourable microbes present within the flour, including spores.